1. Field of the Disclosure
The present invention relates to an LED device, and more particularly, to an LED device that implements an efficient dimming operation.
2. Discussion of the Related Art
LEDs have been used for a variety of applications owing to advantages such as high efficiency, high-speed response, long lifetime, small size, light weight, and energy saving due to low power consumption. And LEDs are environmentally friendly light sources because LEDs do not generate carbon monoxide and are also mercury free.
As luminance efficiency of LEDs has increased recently, LEDs have started to be applied to light source fields to which they have not previously been applied due to luminance constraints. However, an LED lighting device is greatly limited in use since it is generally difficult to implement a dimming function for LEDs, which are driven by current, compared to lighting devices which are driven by voltage.
Reasons why implementing a dimming function for LEDs is difficult will be described in detail with reference to the accompanying drawings.
FIG. 1 shows a block diagram illustrating an apparatus that uses a halogen lamp at an upper portion and shows an operation waveform diagram of the apparatus at a lower portion.
As shown in FIG. 1, the illumination apparatus that uses the halogen lamp includes a halogen ballast 11 that receives 220V power provided from a power source 10 and a halogen lamp 12 that receives a 12V drive voltage provided from the halogen ballast 11. As shown at the lower portion of FIG. 1, the halogen ballast 11 receives a 220V AC voltage 101 and provides an 11 kHz, 12V drive voltage 102. The halogen lamp 12 is driven with the drive voltage 102 received from the halogen ballast 11.
FIG. 2 shows a block diagram illustrating an LED device that uses an LED at an upper portion and shows an operation waveform diagram of the LED device at a lower portion.
As shown in FIG. 2, the LED device includes a halogen ballast 21 that receives 220V power provided from a power source 20 and an LED driver 22 that receives a 12V drive voltage provided from the halogen ballast 21 and drives an LED 23.
The LED driver 22 provides a constant DC current to the LED 23 to drive the LED 23. As shown at a lower portion of FIG. 2, the halogen ballast 21 receives a 220V AC voltage 201 and provides an 11 kHz, 12V drive voltage 202. The LED driver 22 generates a constant current 203 for driving the LED 23 using the 11 kHz, 12V drive voltage 202 and provides the constant current 203 to the LED 23.
FIG. 3 shows a block diagram illustrating an apparatus including a halogen lamp using a triac dimmer and shows an operation waveform diagram of the apparatus at a lower portion.
FIG. 3 illustrates the principle of a dimming operation of a halogen lamp when a widely used triac dimmer is applied to the halogen lamp. Specifically, the apparatus includes a triac dimmer 31 that receives 220V power 301 provided from a power source 30 and a halogen ballast 32 that drives a halogen lamp 33 using a drive voltage 302 provided from the triac dimmer 31. The triac dimmer 31 controls the level of an input voltage by controlling an angle of an input voltage. An intensity of light emitted from the halogen lamp 33 can efficiently be controlled by using the triac dimmer since the halogen lamp 33 is driven by voltage.
FIG. 4 is a block diagram illustrating a method of operating an LED device using a triac dimmer.
As shown in FIG. 4, the LED device includes a triac dimmer 41 that receives 220V power 401, a halogen ballast 42 that generates and provides an 11 kHz, 12V drive voltage 403 using a drive voltage 402 provided from the triac dimmer 41, an LED driver 43 that receives the drive voltage 403 provided from the halogen ballast 42 and generates a constant DC current, and an LED 44 that receives the constant DC current.
The LED device implemented as shown in FIG. 4 can not provide an efficient dimming operation of the LED 44 since the triac dimmer 41 is voltage control type and the LED driver 43 is current control type. A final drive current 404 for driving the LED 44 is pulsed and thus only appears locally. Therefore, the dimming operation of the LED is not continuous (or smooth) and the LED is turned off immediately after flickering.
To overcome this problem, there is a need to develop a new 12V halogen ballast which can implement a continuous or smooth dimming operation or to use an expensive LED driver.